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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % general-entities SYSTEM "../general.ent">
%general-entities;
]>
<sect1 id="ch-scripts-systemd-custom">
<?dbhtml filename="systemd-custom.html"?>
<title>Systemd Usage and Configuration</title>
<indexterm zone="ch-scripts-systemd-custom">
<primary sortas="e-Systemd">Systemd Customization</primary>
</indexterm>
<sect2>
<title>Basic Configuration</title>
<para>The <filename>/etc/systemd/system.conf</filename> file contains a set
of options to control basic systemd operations. The default file has all
entries commented out with the default settings indicated. This file is
where the log level may be changed as well as some basic logging settings.
See <filename>systemd-system.conf(5)</filename> manual page for details on
each configuration option.</para>
</sect2>
<sect2>
<title>Disabling Screen Clearing at Boot Time</title>
<para>The normal behavior for systemd is to clear the screen at
the end of the boot sequence. If desired, this behavior may be
changed by running the following command:</para>
<screen role="nodump"><userinput>mkdir -pv /etc/systemd/system/getty@tty1.service.d
cat > /etc/systemd/system/getty@tty1.service.d/noclear.conf << EOF
<literal>[Service]
TTYVTDisallocate=no</literal>
EOF</userinput></screen>
<para>The boot messages can always be revied by using the
<userinput>journalctl -b</userinput> command as the root user.</para>
</sect2>
<sect2>
<title>Disabling tmpfs for /tmp</title>
<para>By default, <filename class="directory">/tmp</filename> is created as
a tmpfs. If this is not desired, it can be overridden by the following:</para>
<screen role="nodump"><userinput>ln -sfv /dev/null /etc/systemd/system/tmp.mount</userinput></screen>
<para>This is not necessary if there is a separate partition for
<filename class="directory">/tmp</filename> specified in
<filename>/etc/fstab</filename>.</para>
</sect2>
<sect2>
<title>Configuring Automatic File Creation and Deletion</title>
<para>There are several services that create or delete files or
directories:</para>
<itemizedlist>
<listitem><para>systemd-tmpfiles-clean.service</para></listitem>
<listitem><para>systemd-tmpfiles-setup-dev.service</para></listitem>
<listitem><para>systemd-tmpfiles-setup.service</para></listitem>
</itemizedlist>
<para>The system location for the configuration files is
<filename>/usr/lib/tmpfiles.d/*.conf</filename>. The local
configuration files are in
<filename class="directory">/etc/tmpfiles.d</filename>. Files in
<filename class="directory">/etc/tmpfiles.d</filename> override
files with the same name in
<filename class="directory">/usr/lib/tmpfiles.d</filename>. See
<filename>tmpfiles.d(5)</filename> manual page for file format
details.</para>
</sect2>
<sect2>
<title>Overriding Default Services Behavior</title>
<para>A systemd service contents can be overriden by creating a directory
and a configuration file in <filename
class="directory">/etc/systemd/system</filename>. For example:</para>
<screen role="nodump"><userinput>mkdir -pv /etc/systemd/system/foobar.service.d
cat > /etc/systemd/system/foobar.service.d/foobar.conf << EOF
<literal>[Service]
Restart=always
RestartSec=30</literal>
EOF</userinput></screen>
<para>See <filename>systemd.unit(5)</filename> manual page for more
information. After creating the configuration file, run
<userinput>systemctl daemon-reload</userinput> and <userinput>systemctl
restart foobar</userinput> to activate the changes to a service.</para>
</sect2>
<sect2>
<title>Debugging the Boot Sequence</title>
<para>Rather than plain shell scripts used in SysVinit or BSD style init
systems, systemd uses a unified format for different type of startup
files (or units). The command <command>systemctl</command> is used to
enable, disable, controll state, and obtain status of unit files. Here
are some examples of frequently used commands:</para>
<itemizedlist>
<listitem>
<para><command>systemctl list-units -t <replaceable><service></replaceable> [--all]</command>:
lists loaded unit files of type service.</para>
</listitem>
<listitem>
<para><command>systemctl list-units -t <replaceable><target></replaceable> [--all]</command>:
lists loaded unit files of type target.</para>
</listitem>
<listitem>
<para><command>systemctl show -p Wants <replaceable><multi-user.target></replaceable></command>:
shows all units that depend on the multi-user target. Targets are
special unit files that are anogalous to runlevels under
SysVinit.</para>
</listitem>
<listitem>
<para><command>systemctl status <replaceable><servicename.service></replaceable></command>:
shows the status of the servicename service. The .service extension
can be omitted if there are no other unit files with the same name,
such as .socket files (which create a listening socket that provides
similar functionality to inetd/xinetd).</para>
</listitem>
</itemizedlist>
</sect2>
<sect2>
<title>Working with the Systemd Journal</title>
<para>Logging on a system booted with systemd is handled by
systemd-journald (default), rather than a typical unix syslog daemon.
systemd-journald write log entries to a binary file format, rather than
a plain text log file. To assist with parsing the file, the command
<command>journalctl</command> is provided. Here are some examples of
frequently used commands:</para>
<itemizedlist>
<listitem>
<para><command>journalctl -r</command>: shows all contents of the
journal in reverse chronological order.</para>
</listitem>
<listitem>
<para><command>journalctl -u <replaceable>UNIT</replaceable></command>:
shows the journal entries associated with the specified UNIT
file.</para>
</listitem>
<listitem>
<para><command>journalctl -b[=ID] -r</command>: shows the journal
entries since last successfull boot (or for boot ID) in reverse
chronological order.</para>
</listitem>
<listitem>
<para><command>journalctl -f</command>: povides functionality similar
to tail -f (follow).</para>
</listitem>
</itemizedlist>
</sect2>
</sect1>
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